全文获取类型
收费全文 | 36620篇 |
免费 | 7013篇 |
国内免费 | 3702篇 |
专业分类
化学 | 9008篇 |
晶体学 | 1052篇 |
力学 | 1212篇 |
综合类 | 162篇 |
数学 | 362篇 |
物理学 | 18054篇 |
无线电 | 17485篇 |
出版年
2024年 | 78篇 |
2023年 | 280篇 |
2022年 | 568篇 |
2021年 | 767篇 |
2020年 | 856篇 |
2019年 | 658篇 |
2018年 | 732篇 |
2017年 | 1123篇 |
2016年 | 1314篇 |
2015年 | 1496篇 |
2014年 | 2050篇 |
2013年 | 2635篇 |
2012年 | 2730篇 |
2011年 | 2583篇 |
2010年 | 2011篇 |
2009年 | 2280篇 |
2008年 | 2598篇 |
2007年 | 2648篇 |
2006年 | 2621篇 |
2005年 | 2326篇 |
2004年 | 2053篇 |
2003年 | 1892篇 |
2002年 | 1565篇 |
2001年 | 1509篇 |
2000年 | 1355篇 |
1999年 | 1057篇 |
1998年 | 912篇 |
1997年 | 855篇 |
1996年 | 709篇 |
1995年 | 624篇 |
1994年 | 554篇 |
1993年 | 455篇 |
1992年 | 366篇 |
1991年 | 287篇 |
1990年 | 213篇 |
1989年 | 133篇 |
1988年 | 99篇 |
1987年 | 77篇 |
1986年 | 41篇 |
1985年 | 48篇 |
1984年 | 36篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1975年 | 11篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
141.
Waveband switching (WBS) is a promising technique to reduce the switching and transmission costs in the optical domain of a wavelength-division multiplexing (WDM) network. This paper considers the problem of provisioning dynamic traffic using WBS in a WDM mesh network. The network of interest is a homogeneous WBS network, where each node has the functionality of WBS. The problem is called the dynamic WBS problem, which involves searching waveband-routes or wavelength-routes for the dynamically arriving traffic requests. The objective is to minimize the total switching and transmission costs in the optical domain. To solve the dynamic WBS problem, an auxiliary graph model capturing the network state is proposed. Based on the auxiliary graph, two heuristic on-line WBS algorithms with different waveband grouping policies are proposed, namely the wavelength-first WBS algorithm based on the auxiliary graph (WFAUG) and the waveband-first WBS algorithm based on the auxiliary graph (BFAUG). Simulation results indicate that WBS is an attractive technique which reduces the overall switching and transmission costs by up to 30% in the network. The results also show that the WFAUG algorithm outperforms the BFAUG algorithm in terms of port savings and cost savings. 相似文献
142.
An all-optical fiber nonlinear Fabry-Perot resonator is proposed. The steady-state model for describing this resonator is developed. The transmission and refection bistabilities are shown numerically. Our results show that the bistability in this system is similar to that in a normal nonlinear Fabry-Perot etalon, except that the characteristics of the bistability can be changed not only by the cavity length but also by the phase shifts of the fiber loop mirrors. 相似文献
143.
Changes in thin zinc-sulfide films under the action of the γ-radiation of Co60 are studied by investigating electroluminescence spectra of terbium embedded in these films as a luminescent probe. It is
shown that changes in the relation of the intensities of bands, a decrease in their halfwidth and the background component,
and simplification of the spectrum are observed in a short-wave region of the Tb radiation spectrum that corresponds to5D3→7Fj transitions. The same modification of the radiation spectrum is characteristic of ZnS films whose crystalline structure is
ordered in the course of thermal annealing at a temperature of 350°C. Based on the analysis of the data obtained it is inferred
that irradiating the ZnS films with small radiation doses of 104–105 rad leads to the ordering of their crystalline structure due to the elimination of one of the types of structural defects.
Institute of Physics of Semiconductors, National Academy of Sciences of Ukraine, 45, Nauka Ave., Kiev-28, 252650. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 338–341, May–June, 1997. 相似文献
144.
In this paper, we examine, both experimentally and theoretically, the kinetics of formation and microstructure of product
phases in thin film reactions, using the Nb/Al and Ti/Al systems as our prototypes. The results of calorimetry and microscopy
studies are interpreted using simple kinetic and morphology models. In particular, the kinetic models employed here focus
on the nucleation and growth components of the phase formation process and the morphology models provide a starting point
for the classification of product grain structures.
An erratum to this article is available at . 相似文献
145.
146.
147.
提出了折射率温敏式光纤温度传感器的理论模型,包括子午光线和偏射光线的影响,讨论了多模光纤的弯曲损耗,理论的分析和结果与实验相当一致。 相似文献
148.
149.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献
150.
1IntrodctionThesdV8fltsg6Sofffi1CY0bCfldf山CY0ptlCS6fiS0f8f6lflt6llSltyffiDdU18tlflgsliddCtCCtlflg,simpletechnique,highrellabllltyandlowprice,thereformlcrobendfiberoptlcsensorIswidelyusedtomeasurementofstrain,stressandv比rationetc.Inpractice,thesensltlvltyofsensorIsaveryimportantparameter,andthesensltlvltyofmlcrobendf山eroptlcsensorIsmainlyrelat-6dtofoil0WlflgthY66f8CtofS[‘-:ffilCfob6fldsffiplltlld6:fillffib6yofthlCY0b6fldS6Ct10llSsfldffil-crobendperiod,andmlcrobendperio… 相似文献